A conventional brake control apparatus for a vehicle applies braking force to wheels by utilizing a hydraulic pressure of a brake fluid, air pressure and the like as a pressure source. In the conventional brake control apparatus, when a brake fluid leakage or air leakage occurs, a malfunction such as failure of applying the braking force to the wheels may be induced. Therefore, the conventional brake control apparatus is configured to detect a malfunctioning state of the braking force and controls the braking force applied to a wheel that is not malfunctioning in order to stop the vehicle safely.
For example, JP1996-282465A discloses a brake control apparatus that detects a malfunction of a wheel to which a hydraulic pressure control based on an anti-skid control is executed. The brake control apparatus disclosed in JP1996-282465A determines that the anti-skid control is not executed with regard to the wheel subjected to the anti-skid control in a case where a wheel speed of the anti-skid control subject wheel is greater than a wheel speed of a wheel to which the anti-skid control is not executed, contrary to the fact where the wheel speed of the anti-skid control subject wheel becomes generally equal to or less than the wheel speed of the wheel to which the anti-skid control is not executed. As a result, the brake control apparatus disclosed in JP1996-282465A determines that the anti-skid control subject wheel is in the malfunctioning state. As mentioned above, the brake control system disclosed in JP1996-282465A detects the malfunction by comparing wheel a speed of two wheels.
However, an unpredictable difference may occur in the wheel speed of each wheel because of a diameter of a tire attached at each wheel, distribution of the braking force to each wheel, a load applied to each wheel, and effectiveness of brake achieved by abrasion of a brake pad of each wheel may vary. Therefore, comparison between the wheel speeds of two wheels as is disclosed in JP1996-282465A may induce a false detection of the malfunction of the braking force.
A need thus exists to provide a brake control apparatus which is not susceptible to the drawback mentioned above.